1. Field of the Invention
The present invention relates an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer, and particularly to a toner supplying device used therein for supplying toner to a developing device which develops an electrostatic latent image on an electrostatic latent image carrying member.
2. Description of the Related Arts
Such toner supplying devices have been known that can merely supply new toner to a developing device and that can supply not only the new toner but also collected toner which is collected by a cleaner from an electrostatic latent image carrying member by recycle means.
The means for recycling the toner, which is collected by the cleaner, to the developing device is disclosed in the Japanese Examined Patent Publication No. 63-45113, and the Japanese Laid-Open Patent Publication Nos. 55-73078, 55-103578 and 56-66884.
According to summarized contents of these publications, resupplying of the collected toner is performed by (a) supplying the collected toner without processing, (b) supplying the collected toner without processing when new toner is not supplied, and supplying the collected toner together with the new toner when the new toner is supplied in response to a new toner feed instruction signal sent from appropriate means such a toner density sensor or an image density sensor, or (c) supplying the collected toner after applying to it corona charging of the same polarity as the toner polarity at a developing section when it is located on an electrostatic latent image carrying member (Japanese Examined Patent Publication No. 63-45113).
However, the toner generally includes various kinds of additives or particles stuck thereto. Such additives and particles may include a fluidization agent such as silica, aluminium oxide, titanium oxide or magnesium fluoride; chargeable particles of silica, titanium oxide or the like to which coupling processing has been applied by chargeable monomer (e.g., monomer having amino group or fluorine atom); resin beads serving as a cleaning assistant, an abrasive for removing a deteriorated layer on a surface of a photosensitive member; or other additives such as releasing agent for improving fixing ability. Owing to these additives, condensation of the toner is prevented. Further, if two-component developer is used, frictional chargeability of the toner with respect to carrier in the developing device is improved. If monocomponent developer is employed, the frictional chargeability with respect to a toner restricting member which contacts a toner carrying and feeding member of the developing device is improved.
However, after the toner was once used for developing, the additives have moved to the carrier and further from the carrier to the electrostatic latent image carrying member, and have been substantially removed from the surfaces of the toner particles.
Therefore, the collected toner contains extremely small amount of additives sticking thereto. Consequently, if the collected toner were reused without processing, there would be possibility that the essential effect of the additives could not be obtained, and specifically, deterioration of fluidity of the toner, condensation of the toner and deterioration of the frictional chargeability of the toner would be caused. As a result of the deteriorated chargeability, there may be caused dispersion of the toner and fogging, i.e., sticking of the toner to an image background on a recording material.
In spite of disadvantages described above, the resupplying of the collected toner in the prior art is performed by returning the collected toner, from which the additive has substantially disappeared, into the developing device without any processing, so that the fogging and/or the dispersion of the toner are caused.
Even when the new toner is supplied and the collected toner is supplied together with it, it is impossible to expect that the additive of the new toner sufficiently sticks to the collected toner because the new toner and the collected toner are not positively mixed prior to supplying. Further, the collected toner is supplied without processing when the new toner is not supplied. Moreover, the collected toner, which passed developing and transferring sections and a cleaning section in which it contacts, e.g., a cleaning member, has frictional charging characteristics which is extremely different from those of the new toner which has not passed the above sections, resulting in unstable quality of finished images.
Even in such a case that the collected toner is subjected to the corona charging of the same polarity as the toner polarity at a developing section, as described above, uniform charging cannot be expected, which may cause the fog and unstable quality of finished images, because the additives have hardly stuck to the collected toner.
Accordingly, it is an object of the invention to provide an improved device for supplying toner to a developing device in an electrophotographic image forming apparatus, and particularly to provide a toner supplying device in which, not only new toner but also toner collected by a cleaner can be supplied and resupplied, respectively, and further a toner fluidity and a toner chargeability can be improved in the collected toner by sticking an additive to it prior to resupplying, whereby condensation of the toner, fog in an image and dispersion of the toner can be sufficiently prevented without other countermeasures.